The present invention provides low-power electric contacts, particularly contacts for switching and plug-in connection, which are made of a composite material comprising a base material and an outer contact layer of precious metals.
Electrical contacts, and particularly those having to meet the rigorous requirements involved in switching applications and plug-in applications, generally utilize noble metals or alloys of noble metals as the contact layer which is clad onto a substrate or base which is not made of noble metals. The base or substrate metals are usually copper alloys, for example, copper-tin, copper-zinc, copper-zinc-nickel, copper-tin-nickel, and copper-beryllium. Nickel and iron alloys are also used as the base material for contacts.
In the manufacture of such composite materials, the outer contact layer and the substrate material are selected from alloys which have properties and characteristics essential to the basic production methods which are sufficiently close to each other so that during processing and also service, the thermal and mechanical stresses do not crack the contact or cause separation between the contact layer and the substrate, instead, leaving them solidly bound to each other.
German Pat. No. 10 89 491 discloses a contact layer for low-power contacts particularly suitable in telecommunication technology having a contact layer of an alloy comprising 25-35% palladium, 35-45% silver, and 25-35% gold.
Alloys for electric contacts which contain palladium, silver and gold as the principal components, are also disclosed to contain indium and tin, together with additional components; see, for example, German Pat. No. 25 40 956 (corresponding to U.S. Pat. No. 4,069,370) disclosing an alloy containing 20-30% by weight palladium, 15-25% silver, 2.5-5% tin, 0.05-0.5% iridium, 0.05-0.5% ruthenium, 0.05-0.5% copper, 0.1-2% indium, and the balance gold; and German Pat. No. 26 37 807 (corresponding to U.S. Pat. No. 4,111,690) disclosing an alloy containing 10-40% silver, 2-25% palladium, 1-5% nickel, 0.1-10% indium, 0.1-3% tin, and the balance gold.
It is an object of the present invention to provide a low-power electric contact particularly suitable for switching and plug-in connections which has improved mechanical and electrical characteristics as a contact, together with a strong bond strength between the contact layer and the substrate.